1. Field of Invention
The present invention is directed to an ink composition, and methods of making and using the ink composition. More specifically, the present invention is directed to fast drying ink jet ink containing alkyl saccharide surfactants, and methods of making and using such inks.
2. Description of Related Art
Ink jet printing is a non-impact printing method that produces droplets that are deposited on a print substrate (recording medium) such as plain paper, coated paper, transparent film (transparency), textile, or the like in response to electronic digital signals. Thermal or bubble jet drop-on-demand ink jet printers have found broad applications as output for personal computers in the office and at home.
In existing thermal ink jet printing processes, the print head typically comprises one or more ink jet ejectors. Each ejector includes a channel communicating with an ink supply chamber or manifold at one end, and having an opening at an opposite end referred to as a nozzle. A thermal energy generator, usually a resistor, is located in each of the channels at a predetermined distance from the nozzles. The resistors are individually addressed with a current pulse to shortly vaporize the ink within each respective channel to form a bubble that expels an ink droplet. As the bubble grows, the ink rapidly bulges from the nozzle and is shortly contained by the surface tension of the ink as a meniscus. This is a temporary phenomenon, and the ink is quickly propelled toward a print sheet.
As the bubble begins to collapse, the ink remaining in the channel between the nozzle and the bubble start to move toward the collapsing bubble, causing volumetric contraction of the ink at the nozzle resulting in the separation of the bulging ink from the nozzle as a droplet. The acceleration of the ink out of the nozzle while the bubble is growing provides sufficient momentum and velocity to propel the ink droplet in a substantially straight-line direction towards a print substrate. Subsequently, the ink channel refills by capillary action and is ready for the next repeating thermal ink jet process.
Thermal ink jet process are well known and described in, for example, U.S. Pat. Nos. 4,251,824, 4,410,889, 4,412,224, 4,463,359, 4,532,530, 4,601,777, 5,139,574, 5,145,518 and 5,281,261, the entire disclosures of which are incorporated herein by reference. Because the droplet of ink is emitted only when the thermal energy generator is actuated, this type of thermal ink jet printing is known as xe2x80x9cdrop-on-demandxe2x80x9d printing. Other types of drop-on-demand printing, such as piezoelectric ink jet printing and acoustic ink jet printing, are also known.
Continuous ink jet printing is also known. In continuous ink jet printing systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. Multiple orifices or nozzles can be used to increase imaging speed and throughput. The ink is perturbed while being ejected from an orifice, causing the ink to break up into droplets at a fixed distance from the orifice. At the point of break-up, the electrically charged ink droplets pass through an applied electrode that switches on and off in accordance with digital data signals. Charged ink droplets pass through a controllable electric field that adjusts the trajectory of each ink droplet in order to direct it either to a gutter for ink deletion and recirculation or to a specific location on a recording substrate to create images.
In an ink jet printing apparatus, the print head typically comprises a linear array of ejectors, and the print head moves relative to the surface of the print substrate, either by moving the print substrate relative to a stationary print head, or vice-versa, or both. In some types of apparatuses, at least a relatively small print head supplied with ink moves across a print sheet numerous times in swathes in order to complete an image. For multicolor ink jet printing, a set of print heads supplied with ink (e.g., cyan, magenta, yellow and/or black) can move across the print substrate numerous times in swathes and disperse selected inks in any desired pattern (e.g., xe2x85x9, xc2xc, xc2xd, full tone), according to digital signals.
The speed of this type of single or multiple color ink jet printing on a substrate is determined by the moving speed of the print heads across the print substrate, ink jetting frequency (or frequency response), and the desired number of swathes needed for printing. The printing speed of this type of ink jet apparatus can be increased if two or more print heads are butted together to form a partial-width array print head for printing each ink in a monochrome or multicolor ink jet printing system. The partial-width ink jet print head has more ink jet nozzles per print head, and can deliver a large number of ink droplets across the substrate in a swath in a short period. Monochrome or multicolor ink jet printing apparatuses using one or several partial-width print heads may have a faster printing speed than current commercial ink jet printers.
Alternatively, a print head that consists of an array of ejectors (e.g., several butted print heads to give a full-width array print head) and extends the full width of the print substrate may pass an ink down once onto the print substrate to give full-page images, in what is known as a xe2x80x9cfull-width array printer.xe2x80x9d When the print head and the print substrate are moved relative to each other, image-wise digital data is used to selectively activate the thermal energy generators in the ink jet print head over time so that desired images will be created on the print substrate at a fast speed. For multicolor ink jet printing, several full-width array print heads and inks (e.g., cyan, magenta, yellow and black) can be used to deliver multi-color inks onto a print sheet. This type of multicolor ink jet printing process is capable of printing multi-color images and monochrome color images on a print substrate at a much faster speed than current commercial color ink jet printers.
In current ink jet printing processes, surfactants are used in the ink to decrease the surface tension of the ink for faster penetration into the print substrate. Examples of these conventional surfactants include polyethylene glycol (PEG), polypropylene glycol (PPG), copolymers thereof and polyethylene glycol/polysiloxane copolymers.
Applicants have discovered that known surfactants, in decreasing the surface tension of inks for faster penetration and therefore fast drying, result in a decrease in print quality. Applicants have also discovered that known methods for increasing the speed of penetration (i.e., decreasing ink drying time) result in a decrease in print quality. A decrease in print quality can be seen as increased mid frequency line edge noise (MFLEN) and detrimental optical density (OD) effects. Current surfactants and methods, therefore, sacrifice print quality for an increased drying rate of ink jet inks.
The present invention is directed to an ink jet ink composition that comprises at least one alkyl saccharide surfactant that includes at least one hydrophilic saccharide group head connected to at least one hydrophobic alkyl chain tail. The present invention is also directed to methods of making and using such an ink jet ink composition. Applicants have discovered that such a surfactant at least decreases the surface tension of the ink for faster penetration and a decrease in drying time, while the at least one hydrophobic alkyl chain of such a surfactant at least attaches to the ink pigments, and the at least one saccharide moiety of such a surfactant at least keeps the ink pigments on the surface of the printing substrate, such as paper, through affinity interactions to maintain a high print quality. Ink jet ink compositions according to this invention, and methods of making and using the ink jet ink compositions, provide at least the advantage of an increased drying rate of ink jet inks while maintaining a comparable print quality as compared to known ink jet ink compositions that do not include at least one alkyl saccharide surfactant.